1. Field of the Invention
The present invention generally relates to the Third Generation Partnership Project (3GPP) specification of the Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA) and, more particularly to, a method for minimizing the loss of data and ensuring that large delays do not occur during reconfigurations of an uplink transmission time interval (TTI) length of a WCDMA High Speed Packet Uplink Access (HSUPA) air interface.
2. Description of the Related Art
A key element of the HSUPA feature is high speed WCDMA Base Station (i.e., Node B) level Hybrid Automatic Repeat requests (HARQ), where the Node B immediately acknowledges the reception of transmitted packets at each uplink transmission time interval (TTI) subsequent to any propagation delays, such as Tprop, as illustrated in FIG. 1. In this case, the acknowledgment is either positive or negative. In instances where the packets transmitted at the uplink TTI were incorrectly received, the user equipment (UE) either retransmits the exact same number of bits in the packet or the exact incremental redundancy bits for the same information to be transmitted.
The developers of the 3GPP standard have agreed to established two different uplink TTI lengths (i.e., 2 ms and 10 ms) for the HSUPA air interface, and that the uplink TTI length is to be semi-static, i.e. the change of a HSUPA radio link (or air interface) TTI length requires a synchronous radio link reconfiguration procedure that is controlled by a radio network controller (RNC).
Typically, there are pending transmissions when a change of the uplink TTI length occurs, i.e. the Node B has received a packet incorrectly and has requested a retransmission of the packet. In this case, prior to retransmission of the packet occurring, the uplink TTI length is changed. As a result, a loss of data and/or large delays due to retransmissions by higher protocol layers will occur upon reconfiguration of the uplink TTI length because the packets with pending retransmissions are lost in the physical layer. At present, the 3GPP standard fails to address system behavior during uplink TTI length reconfigurations. Accordingly, there is a need to minimize the loss of data and/or ensure large delays do not occur when the uplink TTI length of the HSUPA air interface is reconfigured.